I went to a couple of building sites and the contractors gave me left over pieces of Header, (used over doors and windows). It is heavy and thick and will support any coach you need it for.
I cut them to 2'x2' or 18"x18" whatever you want and can get and screwed a 2' 2x6 in the center of each and attached a piece of rope to the corner. (drilled a hole).
In winter I put the 2x6 down so it will piviot (rock) and break free from ice, also if in a situation where it may slip i put the 2x6 down. IF on pavement or sand or anything that the jack can sink into I put the header down for stability.
And at over 4" tall they are great for leveling if you cannot find a flat place.
An RV'r is someone driving a $300,000.00 Motorhome towing a $40,000.00 car and looking for a free place to park.